1. Field of the Technique
The present technique relates to a head integrated circuit (IC) that drives a heating element for controlling spacing between a storage medium and a magnetic head, and also relates to a storage apparatus including the head IC.
2. Description of the Related Art
With recent sophistication of information processing technology, it has become important to ensure data reliability. Particularly, in a storage apparatus, the most important function is to reliably record data on a medium. In a magnetic disk apparatus, magnetic data is stored on a magnetic storage medium in response to a reversal of write current generated from data. The stored magnetic data is read by a read head (specifically, a magnetoresistive (MR) head based on a magnetoresistive effect), converted from the magnetic data into electric signal data, and sent to a controller.
When the magnetic disk apparatus proceeds to perform a write operation, first, a write gate signal from the controller causes a read channel to enter write mode and also causes a write current depending on data to flow through a write head.
Under low temperatures, the temperature of the write head is low before the write operation starts. Upon start of the write operation, the temperature of the write head is increased by application of the write current thereto. This causes a transient thermal stress to the magnetic pole of the write head. As a result, the write magnetic pole expands with heat and protrudes toward the storage medium. This is generally referred to as pole tip protrusion (PTP).
Although the magnetic pole does not protrude at the beginning of the write operation, the magnetic pole gradually protrudes as the duration of application of the write current increases. This means that the magnetic spacing between the storage medium and a magnetic head including the write head and the read head is relatively large at the beginning of the write operation, but decreases as the write operation proceeds.
Therefore, the write capability at the beginning of the write operation is lower than that at the end of the write operation. More specifically, the overwrite performance is degraded at the beginning of the write operation. That is, since the ability to overwrite previous data on a track is lower in earlier phases of the write operation, the previous data is observed as noise during the read operation, and thus the error rate is high.
As the write head gradually protrudes, the magnetic head becomes closer to the storage medium and the write operation is performed at a distance closer to the storage medium, so that the overwrite performance is generally improved. In particular, when the magnetic disk apparatus is used in low temperature environment, there is a considerable difference between the temperatures of the write head at the beginning and end of the write operation. That is, under low temperatures, the write performance at the beginning of the write operation is very low.
To improve the overwrite characteristics, there is a method in which, at a point when it is necessary to adjust magnetic spacing (for example, immediately before a write operation), heat power from a heater inside a magnetic head is applied and temporarily increased to reduce the response time of protrusion (see, for example, Japanese Laid-open Patent Publication No. 2004-342151 and US Patent Application Publication No. 2005/0057841A1).
As illustrated in FIG. 1, a known heater drive circuit for driving a heater of the above-described type is a linear control circuit (see, for example, Japanese Laid-open Patent Publication No. 2007-26565). As illustrated, the heater drive circuit passes a current from a current source, via a voltage adjusting resistor 116 and a transistor 118, to a heater (resistor) 100 provided in a head.
To supply a set amount of power to the heater 100, there are also provided a power calculator 112, a digital-to-analog converter (DAC) 110, and a differential amplifier 114. The power calculator 112 monitors the current and voltage levels of the heater 100 and converts them to a power level. The DAC 110 converts a set digital power level into an analog power level. The differential amplifier 114 calculates an error between the power level determined by the power calculator 112 and the set power level obtained by the conversion in the DAC 110. Then, the heater drive circuit controls the transistor 118 according to the error determined by the differential amplifier 114. That is, with feedback control, the amount of power to be supplied to the heater 100 is linearly controlled to the set power level.